Formation of 1,2-dioxetane of tetraphenylethylene (TPE) occurs via formation of the electron transfer state of 9-mesityl-10-methylacridinium ion (Acr(+)-Mes) under visible light irradiation, followed by electron transfer from TPE to the Mes(center dot+) moiety together with electron transfer from the Acr(center dot) moiety to O-2, and the subsequent radical coupling between TPE center dot+ and O-2(center dot-) to yield the corresponding 1,2-dioxetane. The dioxetane thus formed was isolated using column chromatography. Photooxygenation of stilbene derivatives is also efficiently catalyzed by Acr(+)-Mes, accompanied by efficient cis-trans isomerization, to afford the corresponding benzaldehydes via electron transfer from Acr(center dot)-Mes(center dot+) to stilbene derivatives. and oxygen. (C) 2006 Elsevier B.V. All rights reserved.